Jhiggins94 - 26-8-2021 at 00:58
hi, i have a query and im hoping someone on here could point me in the right direction.
how would one calculate the pH required to make a compound soluble in a given solvent?
say i was extracting a compound from a reaction mixture into a non polar, i wanted to form the freebase, how would i know how high to raise the pH?
any info would be greatly appreciated 
horuse10 - 26-8-2021 at 01:28
You have to check the pKa of your compound of interest to calculate the right pH
Generaly use an excess of acid or base to drive of the compound out of your phase 1 to your phase 2, it doesn't really matter.
The only exception is if you compound can react with the excess of base or acid, in this situation you have to be careful of how much you add and
monitor carefully the pH
Jhiggins94 - 26-8-2021 at 03:43
ok so if the compound had a pKa of 8.2 how would the pH correspond to that ?
so if in doubt just add acid/base dropwise untill it ceases to precipitate or all goes into solution (depending on disired result) then add a touch
more?
horuse10 - 26-8-2021 at 13:55
pH=pKa+log([A-]/[AH])
With this formula you can calculate the proportion of acidic and basic forms with the pKa and a give pH
In practice your approch is right, just add a little more 